Method for co-fabricating strained and relaxed crystalline and poly-crystalline structures

ABSTRACT

One embodiment of the present invention provides a system for co-fabricating strained and relaxed crystalline, poly-crystalline, and amorphous structures in an integrated circuit device using common fabrication steps. The system operates by first receiving a substrate. The system then fabricates multiple layers on this substrate. A layer within these multiple layers includes both strained structures and relaxed structures. These strained structures and relaxed structures are fabricated simultaneously using common fabrication steps.

RELATED APPLICATION

This application hereby claims priority under 35 U.S.C. §119 to U.S.Provisional Patent Application No. 60/380,598, filed on 15 May 2002,entitled “Methods of Co-Fabricating Strained and Relaxed Structures,” byinventors Jeffery J. Peterson and Charles E. Hunt.

GOVERNMENT LICENSE RIGHTS

This invention was made with United States Government support underGrant Nos. N00014-93-C-0114 and N00014-96-C-0219 awarded by the Officeof Naval Research. The United States Government has certain rights inthe invention.

BACKGROUND

1. Field of the Invention

The present invention relates to the process of fabricating integrateddevices. More specifically, the present invention relates to a methodfor co-fabricating strained and relaxed crystalline, poly-crystalline,and amorphous structures during integrated device fabrication.

2. Related Art

Fabrication of integrated devices (integrated circuits, discreteelectronic devices, Micro ElectroMechanical Systems (MEMS), opticalcomponents, materials using silicon-germanium (SiGe) andsilicon-germanium-carbon (SiGeC), and other materials and devices)typically entails growing several layers of material. A commonfabrication technique produces strained or relaxed structures within thelayers to alter the properties of the layers.

For example, strained and relaxed structures are used during fabricationof an integrated device in creating high-speed complementary metal-oxidesemiconductor (CMOS) circuitry. Positive channel metal-oxidesemiconductor (PMOS) devices with compressively strained layers (e.g.SiGe or SiGeC channels) have the desirable quality of being faster thantheir silicon counterparts. However, the opposite is true ofcompressively strained SiGe negative channel metal-oxide semiconductor(NMOS) devices; they are slower than their silicon counterparts. Inorder to obtain fast NMOS devices, strained Si channels are fabricatedover a relaxed (e.g. SiGe or SiGeC) layer (also known as a bufferlayer). The integration of both of these types of devices on a commonsubstrate, however, requires that both strained and relaxed SiGe (orSiGeC) layers be present on that substrate. Unfortunately, currentfabrication techniques do not allow the simultaneous fabrication of bothstrained and relaxed crystalline, poly-crystalline, and amorphousstructures using common fabrication steps.

Hence, what is needed is a method for co-fabricating strained andrelaxed crystalline, poly-crystalline, and amorphous structures withoutthe problems described above.

SUMMARY

One embodiment of the present invention provides a system forco-fabricating strained and relaxed crystalline, poly-crystalline, andamorphous structures in an integrated circuit device using commonfabrication steps. During operation, the system co-fabricates multiplelayers on a substrate. At least one of these layers includes bothstrained structures and relaxed crystalline, poly-crystalline, andamorphous layers, which are fabricated simultaneously using commonfabrication steps.

In a variation of this embodiment, co-fabricating multiple layers on thesubstrate involves first creating a strained, relaxed, poly-crystalline,or amorphous epitaxial layer with a thickness greater than, equal to, orless than a critical thickness on the substrate. Next, the systemmodifies areas of this relaxed epitaxial layer to provide areas for astrained epitaxial layer. This may include removing areas of the relaxedepitaxial layer. The system then creates a strained epitaxial layer witha thickness less than the critical thickness over the exposed portionsof the substrate.

In a further variation, co-fabricating multiple layers on the substrateinvolves first providing epitaxial blocking layers on the substrate todelineate some areas and other areas. The system then forms an epitaxiallayer on the substrate, wherein the epitaxial layer is a strainedepitaxial layer in some areas and is a relaxed epitaxial layer in otherareas. In one embodiment, small areas will be strained while large areaswill be relaxed.

In a further variation, co-fabricating multiple layers on the substrateinvolves first forming an epitaxial layer with a thickness greater than,equal to, or less than a critical thickness on the substrate. Next, thesystem forms a capping layer on some or all areas of the epitaxiallayer. This capping layer provides a strained layer in areas covered bythe cap a relaxed layer in those areas not covered by the cap. Epitaxialblocking layers may be used as capping layers. Capping layers may lieunder, in, or over the epitaxial layer.

In a further variation, co-fabricating multiple layers on the substrateinvolves building up a circuit by repeating a process that first formsan epitaxial layer, and then forms an epitaxial blocking layer overportions of the epitaxial layer. In one embodiment, areas wherecumulative depositions of the epitaxial layer are less than a criticaldimension provide a strained epitaxial layer and areas where cumulativedepositions are greater than the critical dimension provide a relaxed orstrained crystalline, poly-crystalline, and/or amorphous epitaxiallayer.

In a further variation, co-fabricating multiple layers on the substrateinvolves first forming an epitaxial layer with a thickness greater than,equal to, or less than a critical thickness and then treating a selectedarea of the epitaxial layer to create a relaxed or strained crystalline,poly-crystalline, and/or amorphous epitaxial layer in the selected area.Treating the selected area can be accomplished using a light source, ane-beam source, a sound source, a maser, an infrared source, anultrasonic source, another heat source, or another energy source.

In a further variation, co-fabricating multiple layers on the substrateinvolves first forming an epitaxial layer on the substrate, perhapsselecting areas of the epitaxial layer, and then using implantation toprovide energy to relax or strain areas of the epitaxial layer.

In a further variation, co-fabricating multiple layers on the substrateinvolves first forming an epitaxial layer with a thickness greater than,equal to, or less than a critical thickness on the substrate and thenimplanting an element that can prevent relaxation during a subsequenttreatment as well as create crystalline, poly-crystalline, and amorphouslayers.

In a further variation, co-fabricating multiple layers on the substrateinvolves first forming an epitaxial layer with a thickness less than,equal to, or greater than a critical thickness on the substrate and thenimplanting an element into the epitaxial layer that can cause strain orrelaxation during a subsequent treatment.

In a further variation, co-fabricating multiple layers on the substrateinvolves first modifying selected areas of the substrate and thendepositing or modifying an epitaxial layer on the substrate. Thesemodified areas produce either a strained area or a relaxed area.

In a further variation, co-fabricating multiple layers on the substrateinvolves first creating a crystalline, poly-crystalline, or amorphousarea on the substrate and then depositing or modifying an epitaxiallayer on the substrate. The area provides a template for a relaxed orstrained area.

In a further variation, co-fabricating multiple layers on the substrateinvolves first modifying a base material in selected regions of thesubstrate and then depositing or modifying an epitaxial layer on thesubstrate. The modified area produces either a strained area or arelaxed area.

In a further variation, co-fabricating multiple layers on the substrateinvolves first modifying a growth property of an interface with thesubstrate. This can be accomplished using a surfactant, a catalyzer, amaterial, a selective treatment, or by using another method to modifythe growth property of the interface. The system then deposits ormodifies an epitaxial layer on the substrate. The modified area of thesubstrate produces either a strained area or a relaxed area.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A illustrates a substrate with a relaxed layer in accordance withan embodiment of the present invention.

FIG. 1B illustrates an etched cavity within a relaxed layer inaccordance with an embodiment of the present invention.

FIG. 1C illustrates growing a strained layer and a relaxed layer inaccordance with an embodiment of the present invention.

FIG. 2A illustrates a plan view of a relaxed structure and a strainedstructure in accordance with an embodiment of the present invention.

FIG. 2B illustrates a cut view of a relaxed structure and a strainedstructure in accordance with an embodiment of the present invention.

FIG. 3A illustrates a substrate with a strained layer in accordance withan embodiment of the present invention.

FIG. 3B illustrates an epitaxial blocking structure on a strained layerin accordance with an embodiment of the present invention.

FIG. 3C illustrates relaxed layers and a strained layer on a substratein accordance with an embodiment of the present invention.

FIG. 4A illustrates a strained layer on a substrate in accordance withan embodiment of the present invention.

FIG. 4B illustrates using radiation to relax a strained layer inaccordance with an embodiment of the present invention.

FIG. 5 illustrates using ion implantation to provide relaxation energyin accordance with an embodiment of the present invention.

FIG. 6A illustrates a relaxed layer and a strained layer on a substratein accordance with an embodiment of the present invention.

FIG. 6B illustrates implanting small ions to cause a relaxed layer tobecome strained in accordance with an embodiment of the presentinvention.

FIG. 6C illustrates implanting large ions to cause a strained layer tobecome relaxed in accordance with an embodiment of the presentinvention.

FIG. 7A illustrates a plan view of a modified substrate in accordancewith an embodiment of the present invention.

FIG. 7B illustrates growing strained and relaxed layers on a modifiedsubstrate in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled inthe art to make and use the invention, and is provided in the context ofa particular application and its requirements. Various modifications tothe disclosed embodiments will be readily apparent to those skilled inthe art, and the general principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the present invention. Thus, the present invention is notintended to be limited to the embodiments shown, but is to be accordedthe widest scope consistent with the principles and features disclosedherein.

The data structures and code described in this detailed description aretypically stored on a computer readable storage medium, which may be anydevice or medium that can store code and/or data for use by a computersystem. This includes, but is not limited to, magnetic and opticalstorage devices such as disk drives, magnetic tape, CDs (compact discs)and DVDs (digital versatile discs or digital video discs), and computerinstruction signals embodied in a transmission medium (with or without acarrier wave upon which the signals are modulated). For example, thetransmission medium may include a communications network, such as theInternet.

Etch Stop Removal of Epitaxial Layers

FIG. 1A illustrates a substrate 102 with a relaxed layer 104 inaccordance with an embodiment of the present invention. Relaxed layer104 is an epitaxial layer with a thickness greater than a given criticalthickness that has been grown on substrate 102. The critical thicknessis dependent upon the materials used for substrate 102 and relaxed layer104. This critical thickness is known for many materials and, forexample, is assumed to be 80 nm for a certain composition of SiGe on Si.Photoresist 106 is applied to relaxed layer 104 in preparation for anetching step that will etch away portions of relaxed layer 104 that arenot protected. This process is a patterning process, wherein photoresist106 patterns the relaxed layer to provide the desired elements. Theetching step can include selective etching as described in U.S. Pat. No.5,961,877 to Robinson et al.

Note that while these descriptions recite silicon, SiGe, and SiGeC, thepresent invention is applicable to any other material system such as InPon Si, GaAs on Si, etc. Also note that while the figures show flatlayers, both conformal and non-conformal layers in varied orientationsare equally likely. Note that the materials may be crystalline,poly-crystalline, amorphous, etc.

FIG. 1B illustrates an etched cavity within a relaxed layer inaccordance with an embodiment of the present invention. After relaxedlayer 104 has been etched in the areas where photoresist 106 was notapplied, etched cavity 108 is left in relaxed layer 104. Photoresist 106has been removed in preparation for growth of the next layer.

FIG. 1C illustrates growing a strained layer and a relaxed layer inaccordance with an embodiment of the present invention. A thin epitaxiallayer has been grown over the entire surface except where epitaxialblocking structure 112 has been added. Note that strained layer 110 hasbeen grown in etched cavity 108. Note also that relaxed layer 104 hasbeen grown to a greater thickness but still remains relaxed since thethickness of relaxed layer 104 is still greater than the given criticalthickness. Note that treatment may be selective such that layer 104 isnot modified.

Strained layer 110 can be the same material as relaxed layer 104 or canbe a different material. Relaxed layer 104 can be prevented from growingduring the growth of strained layer 110 by using epitaxial blockingstructures on the top surfaces of relaxed layer 104, or by other means.

Mechanical Properties

FIG. 2A illustrates a plan view of a relaxed structure 206 and astrained structure 204 in accordance with an embodiment of the presentinvention. Strained structure 204 has been constructed in a confinedarea within substrate 202, which prevents strained structure 204 fromrelaxing. Relaxed structure 206 as been grown on top of substrate 202.Relaxed structure 206 is not mechanically constrained and can relax ifits thickness is greater than a given critical thickness. Cut line 208is shown to provide a reference for FIG. 2B.

FIG. 2B illustrates a cut view of a relaxed structure 206 and a strainedstructure 204 in accordance with an embodiment of the present invention.Note that strained structure 204 is embedded within substrate 202 whilerelaxed structure 206 is grown on top of substrate 202.

In general, layers may be grown in a confined area, which modifiesstrain. Note that serpentine designs may be used to modify strain in twoor more dimensions. Completely enclosed layers (e.g. quantum lines anddots) may be prevented from relaxing in three dimensions.

Mechanical properties also include area properties, capping layers, andstrained caps. For area properties, the resistance of small areas torelaxation is used to create strained regions of small area, whileregions of large area become relaxed (various stages of non-strain).Epitaxial growth is done in a single step using epitaxial blocks todefine the areas of each region.

Capping layers can increase the critical thickness substantially. Inthis method, a layer with a layer thickness greater than the criticalthickness but less than a critical thickness with capping is depositedover the entire substrate. Capping layers are then added to thosestructures that will be strained while other areas become relaxed.Epitaxial blocks may be used.

When using strained caps, capping layers of different lattice dimensionare used to increase or decrease the critical thickness with capping.When the critical thickness with capping is decreased, the layers may beforced to relax. When the critical thickness with capping is increased,layer thickness may be increased without relaxation.

Blocked Epitaxial Regrowth

FIG. 3A illustrates a substrate 302 with a strained layer 304 inaccordance with an embodiment of the present invention. Strained layer304 has been grown on substrate 302 and has a thickness less than acritical thickness, which causes the strained layer 304 to be strained.

FIG. 3B illustrates an epitaxial blocking structure 306 on a strainedlayer 304 in accordance with an embodiment of the present invention.Epitaxial blocking structure 306 has been applied to areas of strainedlayer 304 that are to remain strained during the step described inconjunction with FIG. 3C.

FIG. 3C illustrates relaxed layers 308 and a strained layer 304 on asubstrate in accordance with an embodiment of the present invention.After applying epitaxial blocking structure 306, epitaxial growth of theexposed areas of strained layer 304 is continued until the thickness ofthese layers is greater than the critical thickness. These areas thenrelax leaving relaxed layer 308. Epitaxial blocking structure 306 isthen removed.

By combining this method with the method described below in conjunctionwith FIG. 7, it is possible to follow the blocking step with a blanketdeposition (which also covers the epitaxial blocking or alternatesubstrates), thereby co-fabricating wholly, or partially strainedstructures in parallel with amorphous, poly-crystalline, or differentlystrained layers. This may be done in a single growth step.

Thermal Annealing

FIG. 4A illustrates a strained layer 404 on a substrate 402 inaccordance with an embodiment of the present invention. Epitaxialblocking structures 406 have been included to isolate portions ofstrained layer 404.

FIG. 4B illustrates using radiation 410 to relax a strained layer 404 inaccordance with an embodiment of the present invention. Radiation 410 isapplied to strained layer 404 through mask 408. Mask 408 selectivelyblocks some of radiation 410 while allowing radiation 410 to reach thecenter portion of strained layer 404. The thermal effects of radiation410 causes the center portion of strained layer 404 to relax becomingrelaxed layer 412. Note that it is also possible to scan radiation 410over selected portions of strained layer 404 rather than using mask 408.Radiation 410 can be radiation from a light source, an ebeam source, asound source, a maser, and infrared source, an ultrasonic source, or anyenergy source that creates thermal effects within strained layer 404.Note that masking may be by other means.

Post Treatment

FIG. 5 illustrates using ion implantation to provide relaxation energyin accordance with an embodiment of the present invention. This methodbegins with a system similar to that shown in FIG. 4A. Strained layer504 is grown on substrate 502. The relaxation energy is provided fromion source 508 through mask 506. Mask 506 allows ion source 508 toprovide relaxation energy to the center area of strained layer 504. Thisrelaxation energy causes the center portion of strained layer 504 torelax becoming relaxed layer 510.

Post Growth Implantation

FIG. 6A illustrates a relaxed layer 606 and a strained layer 608 on asubstrate 602 in accordance with an embodiment of the present invention.Epitaxial blocking structure 604 is used to separate relaxed layer 606and strained layer 608. In this method, different sized ions areimplanted within the various layers to either cause relaxation or tocause strain.

FIG. 6B illustrates implanting small ions to cause a relaxed layer 606to become strained layer 612 in accordance with an embodiment of thepresent invention. Small ion source 610 implants small ions (i.e. B orC) into relaxed layer 606. These small ions cause relaxed layer 606 tobecome strained layer 612.

FIG. 6C illustrates implanting large ions to cause a strained layer 608to become relaxed layer 616 in accordance with an embodiment of thepresent invention. Large ion source 614 implants large ions (i.e. Ge, orIn) into strained layer 608. These large ions cause strained layer 608to become relaxed layer 616.

Substrate Modification

FIG. 7A illustrates a plan view of a modified substrate 702 inaccordance with an embodiment of the present invention. Modifiedsubstrate area 706 is created using any of several methods. Epitaxialblocking structure 704 is used to define modified substrate area 706.The method used to modify the modified substrate area 706 include: basematerial modification, amorphousation, interface properties, and growthproperties.

Base material modification causes the base material in certain areas tobe modified before deposition to create a template that will produce arelaxed or a strained area. For example, Boron implantation followed byan annealing of the base material causes reduced base material latticedimensions leading to a strained area.

Amorphousation causes the base material in certain areas to becomeamorphous before deposition to create a template which will producerelaxed or amorphous layers in the treated areas.

When using interface properties, the base material in certain areas ismodified in selected regions to produce relaxed or strained areas. Anexample of this technique may use an implanted species to affectselected areas through autodoping.

Using growth properties provides modification of interface, substrate,surfactants, catalyzers, etc. These modifications are made in selectedregions to produce relaxed or strained areas. An example of thistechnique includes selective deposition of either surfactant orinterfering species to affect layer deposition.

FIG. 7B illustrates growing strained and relaxed layers on a modifiedsubstrate in accordance with an embodiment of the present invention.Strained layer 708 has been grown on the unmodified portion of substrate702, while relaxed layer 710 has been grown on modified substrate area706. Note that the strained and relaxed areas grown on substrate 702 canbe reversed from that shown depending on the substrate modification usedand the thickness and material used to grow the epitaxial layer.

Note that the techniques described herein work equally well for paralleland serial fabrication. Note also that the expression “differentlystrained” refers to any change in strain, such as compressive not equalto compressive, compressive not equal to tensile, tensile not equal torelaxed. Relaxed layers may have various amounts of relaxation andstrains.

The foregoing descriptions of embodiments of the present invention havebeen presented for purposes of illustration and description only. Theyare not intended to be exhaustive or to limit the present invention tothe forms disclosed. Accordingly, many modifications and variations willbe apparent to practitioners skilled in the art. Additionally, the abovedisclosure is not intended to limit the present invention. The scope ofthe present invention is defined by the appended claims.

1. A method for co-fabricating strained and relaxed crystalline,poly-crystalline, and amorphous structures in an integrated circuitdevice using common fabrication steps, comprising: receiving asubstrate; and fabricating a plurality of layers on the substrate,wherein a layer within the plurality of layers includes one or more of astrained structure and a relaxed structure and wherein the strainedstructure and the relaxed structure are fabricated simultaneously usingcommon fabrication steps.
 2. The method of claim 1, wherein fabricatingthe plurality of layers on the substrate involves: forming a first layerwith a thickness greater than, equal to, or less than a criticalthickness on the substrate, wherein the first layer is a relaxed orstrained layer; treating areas of the first layer to provide areas for asubsequent layer; and forming a second layer, wherein the second layeris a layer of different strain.
 3. The method of claim 1, whereinfabricating the plurality of layers on the substrate involves: providingblocking layers on the substrate to delineate some areas and otherareas; and forming a layer on the substrate, wherein the layer is astrained layer in some areas and wherein the layer is a layer ofdifferent strain in other areas.
 4. The method of claim 1, whereinfabricating the plurality of layers on the substrate involves: forming alayer with a thickness greater than, equal to, or less than a criticalthickness on the substrate; providing a blocking layer on selected areasof the layer; and forming a capping layer on selected areas of thelayer, wherein the capping layer provides a layer with a different levelof strain than other layers.
 5. The method of claim 1, whereinfabricating the plurality of layers on the substrate involves: buildingup a circuit by repeating a process of: forming a layer, and providing ablocking layer; wherein areas where cumulative depositions that are lessthan, equal to, or greater than a critical dimension provide a strainedor non-strained layer, and areas where cumulative depositions aregreater than, equal to, or less than the critical dimension provide alayer of different strain.
 6. The method of claim 1, wherein fabricatingthe plurality of layers on the substrate involves: forming a layer witha thickness less than, equal to, or greater than a critical thickness;and treating a selected area of the layer to create a relaxed layer inthe selected area, wherein treating the selected area can beaccomplished using one of a light source, an e-beam source, a soundsource, a maser, an infrared source, an ultrasonic source, another heatsource, and another energy source.
 7. The method of claim 1, whereinfabricating the plurality of layers on the substrate involves: forming alayer on the substrate; and using implantation to provide energy torelax selected areas of the layer.
 8. The method of claim 1, whereinfabricating the plurality of layers on the substrate involves: forming alayer with a thickness greater than, equal to, or less than a criticalthickness on the substrate; and implanting an element that can modifystrain after a subsequent treatment.
 9. The method of claim 1, whereinfabricating the plurality of layers on the substrate involves: forming alayer with a thickness less than, equal to, or greater than a criticalthickness on the substrate; and implanting an element that can modifystrain after a subsequent treatment.
 10. The method of claim 1, whereinfabricating the plurality of layers on the substrate involves: modifyingselected areas of the substrate; and forming a layer on the substrate,wherein modified areas produce areas of different strain.
 11. The methodof claim 1, wherein fabricating the plurality of layers on the substrateinvolves: creating a modified area on the substrate; and forming a layeron the substrate, wherein the amorphous area provides a template for anarea of different strain.
 12. The method of claim 1, wherein fabricatingthe plurality of layers on the substrate involves: modifying a basematerial in selected regions of the substrate; and forming a layer onthe substrate, wherein a modified area produces an area of differentstrain.
 13. The method of claim 1, wherein fabricating the plurality oflayers on the substrate involves: modifying a growth property of aninterface with the substrate, wherein modifying the growth propertyincludes one of using a surfactant, using a catalyzer material, usingselective treatment, and using another method to modify the growthproperty; and forming a layer on the substrate, wherein a modified areaproduces areas of different strain.